(1) Field of the Invention
The present invention relates to boron doped nanocrystalline diamond and in particular to electrodes which are electrically conductive. In particular the present invention relates to boron doped diamond wherein exposed surfaces are terminated by carbon-hydrogen or carbon-oxygen bonds.
(2) Description of Related Art
High-quality diamond films can be formed with two different morphologies and microstructures, microcrystalline and nanocrystalline. The distinction between these two structures arises from the nominal grain size, which for microcrystalline films is >1 μm and for nanocrystalline films is ˜20 nm, preferably between 1 and 50 nm. Conventional microcrystalline diamond CVD growth uses hydrocarbon-hydrogen (e.g. 1% CH4/99% H2) gas mixtures and it is known under such growth conditions that hydrogen plays a number of critical roles (Gruen, D. M., MRS Bull. 23 32 (1998); Angus, J. C., et al., J. Appl. Phys. 39 2915 (1968); Hsu, W. L., J. Vac. Sci. Technol. A6 1803 (1988); Frenklach, M., J. Appl. Phys. 65 5124 (1989); Butler, J. E., et al., MRS Bull. 23 22 (1998); Zhou, D., et al., J. Appl. Phys., 84 1981 (1998); Jiao, S., et al., J. Appl. Phys. 90 118 (2001)); McCauley, T. G., et al., Appl. Phys. Lett. 73 1646 (1998)). Among these are stabilization of the diamond lattice and removal of sp2-bonded carbon nuclei, when formed, due to preferential gasification over sp3-bonded diamond. Gruen discovered that phase-pure nanocrystalline diamond can be grown from CH4/Ar gas mixtures containing very little or no added hydrogen (Gruen, D. M., MRS Bull. 23 32 (1998); Zhou, D., et al., J. Appl. Phys. B84 1981 (1998); Jiao, S., et al., J. Appl. Phys. 90 118 (2001); McCauley, T. G., et al., Appl. Phys. Lett. 73 1646 (1998); Gruen, D. M., Annu. Rev. Mater. Sci. 29 211 (1999); and Bhattacharyya, S., et al., Appl. Phys. Lett. 79 1 (2001)). There are two kinds of nanocrystalline diamond films often described. The first are films deposited from high CH4/H2 (>3%) gas mixtures. These films have nanometer-sized features due to the high rate of nucleation, but are generally of low quality (so-called “dirty” diamond) with significant levels of secondary nucleation and sp2-bonded carbon impurity phases. The second are films deposited from CH4/Ar (˜1%) gas mixtures. These films consist of randomly oriented, nanometer-sized grains of phase-pure diamond and are generally of higher quality. The grains are on the order of 20 nm in diameter, and the grain boundaries consist of Π-bonded, carbon atoms (ca. 2–4 atoms wide). The physicochemical properties of the grain boundary change the conductivity and are thus controlled by the grain boundary.
WO 02/31891 A1 describes ultrananocrystalline diamond electrodes containing nitrogen as a dopant. The conductivity is primarily between the grains.
U.S. Pat. No. 6,267,866 to Glesener et al discloses microcrystalline diamond electrodes which are boron doped and deposited on mesh supports. The conductivity is primarily between the grains.
There is a need for improved conductivity in nanocrystalline diamond films.